In a fresh air channel, e.g. of a piston engine, upstream of gas exchange valves, closure devices can be used by means of which the respective flow channel can be controlled. The closure device can comprise at least one closure element, e.g. a flap gate or a rotary slide valve which, during operation, rotates permanently about a rotational axis, a so-called rotating closure element. Such a rotating closure element can also be designated as continuously operating closure element or closure element operating with consistent rotational direction, which differs from a discontinuously operating or oscillating closure element which, during operation, is alternately switched between two end positions, namely an open position and a closed position with alternating rotational direction.
By means of rotating closure elements, pressure vibrations can be generated or existing pressure vibrations can be intensified within the flow channel. Positive pressure amplitudes of said pressure vibrations can be utilized in the fresh air channel of the piston engine, e.g., for generating a pulse charging. Negative pressure amplitudes of said pressure vibrations can be used in a different application for adjusting the exhaust gas recirculation rate. It is principally also possible to generate by means of such a rotating closure element, pressure vibrations downstream of gas exchange valves in an exhaust gas channel so as to influence the exhaust gas recirculation rate via the positive pressure amplitudes. Further, it is possible to influence other parameters or components of the piston engine with such closure devices. For example, the vibrations generated in the fresh air channel by means of the rotating closure element can be utilized for influencing the pollutant emission and/or the fuel consumption. Further, by means of the pressure vibrations, the operating behavior of an exhaust gas turbocharger can be influenced.
Important for such permanently rotating closure elements is the adherence or the adjustment of a phase position relative to a reference variable, in particular a reference time or a reference frequency. The rotating closure element runs through a periodically repeating rotation, the movement of which runs through a rotation angle of 0° to 360°. In a piston engine, the rotational movement of the closure element is synchronized, e.g., with the stroke movement of pistons of the piston engine or with switching times of gas exchange valves. This results inevitably in synchronization with the rotational movement of a crankshaft of the piston engine. Thus, e.g., the rotational position or rotational movement of the crankshaft can be used as reference time or reference variable for the phase position of the rotating closure element.
In order to vary the effect of the flow-dynamic processes, which are generated by means of the closure element, on the operation of the piston engine or the operating parameters of the piston engine such as, e.g., exhaust gas recirculation rate, fuel consumption, pollutant emission, or to adapt them to changing operating points, it can be necessary to change the phase position of the rotating closure element relative to the reference variable, thus in particular relative to the crankshaft angle. For example, an opening time of the rotating closure element can be shifted from +10° crankshaft angle by 5° towards early, thus to +5° crankshaft angle, or towards late, thus to +15° crankshaft angle.
Such changes of the phase position are supposed to take place within a time as short as possible so as to be able to perform the adaptation of the closure device to varying operating points of the piston engine as fast as possible. To be able to adapt the phase position of the rotating closure element during the operation, thus in a dynamic manner, relatively high forces and/or torques are required which, for an adequate drive, involves relatively complicated control or feedback control demands.